The broad objective of this research is to understand the physical principles responsible for the organization and properties of planar bilayer membranes (black lipid films). The major purpose of the work is to extend the usefulness of this important model system for studying biomembrane phenomena such as ion transport. The black film promises to play a major role in the isolation and characterization of ion channels and membrane receptors and it is thus important to understand the model system extremely well. The specific objectives of the research are (1) to understand the physical determinants of the bilayer thickness and dielectric coefficient, (2) to develop an operational phase rule for the black film system which will permit the composition and state of the system to be controlled, and (3) to develop electron microscopic methods for examining the structure and organization of the black film system. The methods to be used in the research include optical and electrical measurements of bilayer thickness, differential scanning calorimetry, vapor pressure osmometry, static vapor pressure measurements, and freeze-fracture electron microscopy.